Carburetor



May 22, 1956 s. F. HUNT 2,746,439

CARBURETOR Filed May 26, 1934 3 Sheets-Sheet 1 L1 I I 54" 6/ /a Ill 2 f/ Z INVENTOR.

jcoff F Hum ATTORNEY May 22, s T

CARBURETOR Filed May 26, 1934 3 Sheets-Sheet 2 2 [NI EA TOR.

Y B fifw ATTORNEY May 22, 1956 s. F. HUNT 2,746,439

CARBURETOR Filed May 26, 1934 3 Sheets-Sheet 3 IN V EN TOR.

A TTORNEY United rates CARBURETOR Scott F. Hunt, South Bend, Ind., assignor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware 4 Claims. or. 123-119 This invention relates to carburetors, and has for its principal object the provision of a choke valve or a carburetor air control which is automatically controlled by the. temperatures and pressures developed by the engine in its operation.

Internal combustion engines using liquid fuel are ordinarily equipped with carburetors having manually operated choke valves for closing the air supply and enriching the fuel mixture for starting the engine. Various means have heretofore been employed to actuate the choke automatically, but since the need for variation in the fuel mixture is dependent on a number of variables, including engine heat, manifold suction and other factors, the automatic chokes that have been previously devised do not entirely meet the requirements.

An object of the present invention is to provide a carburetor choke valve control which is completely automatic and which is actuated by the temperatures developed by the engine and by the relative pressures anterior to the choke valve, between the choke valve and the throttle, and posterior to the throttle.

An important feature of the invention consists in the actuation of the choke valve by the differential of pressures anterior and posterior to the choke valve, the actuation being modified by the temperature of the engine, and the opening movement of the choke valve being conditioned on a predetermined suction posterior to the throttle.

When cranking a cold engine preparatory to starting, it is desirable to limit the air admitted to the carburetor to a minimum in order to supply a rich mixture to the cylinders, but immediately an explosion occurs a greater amount of air should be admitted to prevent the engine stalling from the mixture becoming too rich. As the motor warms up, it is desirable to gradually increase the ratio of air to fuel until the choke valve is fully opened The present invention provides an apparatus which functions in the manner just outlined, the apparatus being illustrated in the accompanying drawings, in which:

Figure 'l is a plan view of a carburetor and associated mechanism embodying the invention;

Figure 2 is a vertical sectional view of the same;

Figure 3 is a detail view showing the thermostat and associated parts;

. Figure 4 is a diagrammatic sectional view showing a modified form of the invention;

Figure 5 is a sectional view showing a further modification;

Figure 6 is a section on the line 6-6 of Figure 2 looking upward and showing the toggle in its broken position; and

Figure 7 is a diagrammatic view representing the embodiment illustrated in Figures ,1 and 2.

The carburetor shown in Figures 1, 2 and 7 is of the down-draft type and comprises an air horn 10 communicating with a carbureting passage 104 which is connected to the intake manifold 14 of the engine. A

atentf throttle 106 is mounted in the carbureting passage adjacent its outlet 107, and is controlled by any suitable known mechanism, indicated generally at 16 in Figure 2. Fuel is supplied to the carburetor through a main fuel nozzle 108 which communicates at 109 with a float chamber 12 and terminates within a primary venturi mounted in co-operative relation to a secondary venturi 112. The fuel nozzle may be air bled through an air inlet 114 which leads to a passage 116 which communicates with the fuel nozzle through a plurality of ports 118. I

The idling fuel is drawn from fuel nozzle 108 to a fuel well and thence through idling passage 122 to ports 124 and 126 positioned respectively anterior and posterior to the throttle. Air is bled into the idling fuel from an inlet 128 which communicates with the carbureting passage at any convenient point. The air horn is provided with a choke valve 18 which is fixed to a shaft 29 mounted in the air horn. Valve 18 is unbalanced by reason of shaft 20 being positioned at a distance from the axis of the air horn so that the differential of air pressure on the opposite faces of the valve will tend to open it inwardly. The choke valve is also provided with a poppet valve 22 of known construction designed to be opened by air pressure to admit a limited amount of air when the choke valve is fully closed. It will be understood that the poppet valve may be omitted if desired, and the carburetor may be of the tip-draft or other type.

An arm 24 is fixed to shaft 20 and has a pivotal connection with a link 26 which is connected with the choke control, to be described.

A casing 28 is mounted on the inlet manifold adjacent the carburetor by means of screws 29 and has a cylinder 30 formed therein which communicates through a check valve, having a movable valve member 32, and a port 34 with the interior of the manifold 14. When the engine is not running, valve member 32 is maintained in its uppermost position by spring 36, but is moved by suction to the position shown in Figure 2 when the motor begins to fire, further downward movement being prevented by spaced tongues 38 on the rim of an outlet plug 410. In case of an explosion within the inlet manifold, valve member 32 moves to its uppermost position, thereby preventing fouling of the apparatus by burnt gases.

A piston 42 is reciprocably mounted in cylinder 30 and is normally held in its uppermost position by a compression spring 44. A link 46 is connected by a ball and socket joint to the piston and at its other end is pivotally connected to a lever 48 which is pivoted to the wall of casing 28 and has a rounded end 50 designed for a purpose to be described. A threaded plug 52 in the easing permits piston 42 to be inserted and removed and has a boss 53 serving as a stop to limit the movement of lever 48. I

The casing 28 is formed with an extension 54v in which is journalled a transverse shaft 56. The outer end of extension 54 has mounted thereon a cup 58 the open face of which lies adjacent the exhaust manifold 60 or any convenient part of the engine which is subject to varying temperatures. The cup 58 may be rotated for adjustment relative to the extension 54, and may be maintained in its adjusted position by means of a screw 61.

A coiled bimetallic element 62 has its inner end secured to shaft 56, as by welding, and has a hooked outer end 63 engaging a pin 64 fixed to the cup 58. Element 62 is so constructed that it tends to straighten when heated, and is so biased that when cold it lies in he position shown in full lines in Figure 3, in which position it exerts a clockwise torque on shaft 56 and a downward reaction on pin 64. As the temperature rises this torque diminishes to zero and at extremely high temperatures the end 63 may disengage pin 64 and move to the position indicated in dotted lines in Figure 3. The element 62 is therefore under a slight bending stress when it is cold and is. under no bending stress at high temperatures.

The other end of shaft 56 has fixed thereto an arm 66 which is pivotallyconnected to link 26. An arm 68 is also fixed to shaft 56 within the casing and at its outer end is pivoted to a link 70 which in turn is pivoted by means of a pin 71 to a link 72 which has its upper end pivoted at 73 to the inner wall of the casing. Links 70 and 72 thus constitute a toggle mechanism and, upon upward movement of arm 68 under the influence of air pressure on the choke valve 18, they may move to the position indicated in dotted lines in Figures 2 and 7. When arm 68 is left free to move downwardly, links 7% and 72, due to their position with respect to each other, move under the influence of gravity and of the element 62 to a position approaching alinement, this movement being limited by an adjustable stop 74 positioned adjacent pin 71. When. inthis position, the force exerted by arm 68 due to pressures developed in cranking the engine cannot move the toggle out of its position, since the links thereof are so close to their dead center position that the friction of the parts cannot be overcome by the relatively slight force due to the suction developed in cranking.

In operation, assuming the engine is cold and being cranked, the parts are in the position shown in Figures 1, 2 and 3, the choke valve being maintained in its fully closed position, against the air pressure tending to open it, by the toggle mechanism which prevents shaft 56 from rotating. The suction developed in the manifold by cranking is insufficient to actuate piston 42, hence air enters the carburetor only through the poppet valve 22.

When an explosion occurs in the cylinders, however, the manifold suction becomes greaterand draws piston 42 downwardly against the force of spring 44, causing the end 50 of lever 48 to move pin 71 to the right well beyond its dead center position, leaving shaft 56 free to rotate. The choke valve then opens under the influence of the differential of pressure on its opposite faces, the only retarding force acting on the choke valve being that of the thermostatic element 62, which While cold exerts a torque on shaft 56 tending to close the choke valve.- This results in the choke valve being maintained in an intermediate position representing a balance between the opening force of the air stream and the closing force of the thermostat.

This condition obtains until the exhaust manifold 60 becomes heated, whereupon the temperature of element 62 gradually rises and the element tends to straighten and exerts a decreasing torque on shaft 56, until when the motor is fully warmed up the end 63 of element 62 has moved to the dotted line position of Figure 3 so that the thermostat has no eifect on the operation of the choke valve, which remains fully open as long as the engine is running.

If desired, the usual manual operating means for the choke valve may also be connected thereto, such construction, as shown in Figure 1, comprising an arm 76 secured to the shaft by an'overrunning connection and pivotally connected with a lever 78 extending to the drivers position.

When the motor is stopped, piston 42 rises to its uppermost position, and the thermostat gradually returns to its original position as the engine cools. The toggle links are moved to the position shown in Figure 2 by the thermostat and by gravity, thus preparing the mechanism for another starting operation.

In the modification shown in Figure 4, the choke valve 80 is mounted in the air inlet 81 in the usual manner and is fixed to a shaft 82 which is provided with an actuating lever 84. A toggle mechanism comprising links 86 and 88 is connected respectively to the arm 84 and a pin 90 mounted on the air horn. A stop 92 projects from the differences in construction hereafter pointed out.

outer wall of the air horn and is so positioned as to prevent links 86 and 88 from moving downward into alignment, while permitting them to approach alignment rather closely. A light spring 94 is connected to the outer end of arm 84 to tend to move the choke valve into closed position, and a second spring 96 is connected to link 88 to tend to move the links into alignment, the other end of the spring being connected to any convenient part of the carburetor, such as the pump arm 98. A thermostat may be connected to the shaft 82 to function in the same manner as the thermostat described in connection with Figures 1, 2 and 3. V

In this modification also, the parts are so designed relative to each other that the suction developed by cranking is insufiicient to cause arm 54 to break the toggle, but when explosions begin to occur in the cylinders, the suction increases to the point where arm 84 breaks the toggle, moving the links 86 and 88 to the position indicated in dotted lines, after which the choke valve is maintained in an intermediate position determined by the force of sucton and the torque of the thermostat.

The modification shown in Figure 5 is similar in principle to that shown in Figures 1 and 2, but with the The casing of the choke control is formed of a base section 90, designed to be bolted to the intake manifold, and a removable cover 92, fitted on the base section. A bell crank lever 94 is keyed to shaft 56 and has a lower arm 96 which is designed to contact with an adjustable stop formed by a screw 98 threaded in a boss 100 formed integral with the base section, and cut away as indicated at 101 to permit outward movement of the upper arm of lever 94. A spring 102 holds screw 98 against accidental rotation. Lever 94 is pivoted at 104 to a link 106 which in turn is pivoted to an arm 108 fixed to an upper shaft 110. Shaft 110 is journaled in standards 112, formed integral with the base section, and has a lever 114, similar to lever 48 of Figure 2, journaled thereon. The lever 114 is designed, upon actuation of piston 42 to, move link 106 and lever 94 out of the position approaching alinement shown in Figure 5. An arm 116 is fixed to shaft 110 and connects with link 26 in the same manner as arm 68 of Figures 1 and 2.

Although the invention has been described with reference to particular embodiments thereof, it will be understood that it may be modified in many ways without departing from the spirit thereof. Thus, the thermostat may if desired be omitted from the embodiments shown in the drawings, the casing 28 may be mounted in any convenient position and connected by a conduit with the manifold, the choke valve may be of the poppet rather than the butterfly type, and the alignment and proportions of the parts may be modified as desired.

This application is a continuation of Hunt et a1. application, Serial No. 575,025, filed November 14, 1931, for Carburetors, now abandoned.

I claim:

1. In an internal combustion engine, a carburetor in which there is incorporated a choke valve, an element actuated by variations in temperature of the engine operatively connected to the choke valve, means adapted to lock the choke valve in closed position, and means independent of the mentioned element to unlock the choke valve.

2. In an internal combustion engine, a carburetor in which there is incorporated a choke valve, a passage connecting the carburetor with cylinders of the engine, an element actuated by variations in temperature of the engine operatively connected to the choke valve, means adapted to lock the choke valve in closed position, and an element actuated by variations in pressure within the passage to unlock the choke valve.

' 3. In ,a carburetor, means forming a mixing conduit, a chokevalve controlling the admission of air to said mixing conduit, said choke valve having a part which is movable toward open position by direct action of suction, suction operated means for opening said choke valve 21 limited distance only, said suction operated means being constructed and arranged to permit a continuance of the opening of said choke valve after the cessation of movement of said suction operated means, and a heat responsive element connected to said choke valve to control the same in conjunction with said suction operated device.

4. In a carburetor, means forming a mixture conduit, a choke valve controlling admission of air to said mixing conduit, said choke valve being movable toward open position by direct action of suction, suction operated means for opening said choke valve a limited distance only, said suction operated means being constructed and arranged to permit a continuance of the opening of said choke valve References Cited in the file of this patent UNITED STATES PATENTS 1,894,354 Kommer et a1. Jan. 17, 1933 1,915,851 Ericson June 27, 1933 2,085,351 Coffey June 29, 1937 2,154,090 Holmes et al Apr. 11, 1939 2,226,580 Perrine Dec. 31, 1940 2,309,419 Sisson Jan. 26, 1943 2,325,372 Coffey July 27, 1943 

